Conventionally, in lamps, such as vehicle lamps, or optical appliances, such as monitoring cameras, condensation of moisture in the inside of a housing containing components, such as a light source, and fogging of a lens associated with the condensation have been a problem.
In Patent Document 1, there is disclosed a technique in which a casing is provided with multiple ventilation holes for preventing condensation in the inside of the housing in a vehicle lamp, to thereby perform ventilation in the inside of the housing by air convection generated in the inside of the housing.